1. Field of the Invention
The present invention relates to the field of printing and in particular, to systems and methods for rendering images in print devices.
2. Description of Related Art
Imaging models such as those provided in Adobe's PDF™ often include the notion of transparency. With opaque objects the topmost object completely obscures the overlapping portions of any underlying object. When imaging models permit transparency, the color of a point on a page may be determined by potentially combining the colors of all objects enclosing the point in a blend-mode according to transparency-model specified compositing rules.
When an object is placed on a page, the object may be composited with a backdrop. Conceptually, the backdrop can be thought of as the result of compositing all previously specified objects. Compositing an object with its backdrop involves blending the objects color with the color of the backdrop at each point. Two parameters, termed shape and opacity determine how an object will be composited with its backdrop. Much like color components, shape and opacity, which vary from 0 to 1, may be specified for each pixel in an object. For opacity, the value 0 implies fully transparent, while 1 implies fully opaque. For shape, 0 indicates that a point lies outside an object with a sharp well-defined edge, while 1 indicates that the point lies inside the object. Values between 0 and 1 may be used in connection with objects with amorphous or soft edges.
The opacity of the object and the opacity of the backdrop determine their respective color contributions to blended and composited colors. Next, the object's shape determines the extent to which the composite color replaces the backdrop color. In some imaging models, one or more consecutive stack objects may be grouped and opacity and shape may be associated with the group thereby affecting blending and compositing operations that pertain to the group as a whole. When the group is composited, the color result of compositing the group may be converted to a luminosity value for each group pixel, which may be associated with the group as a “soft mask”. Thus, the soft mask can be used for shape or opacity values pertaining to an object or a group when additional compositing operations are performed. The soft mask is often used for soft clipping, where the shape of an object or group is modified. Soft clipping can produce effects such as a gradual transition, fading etc. between an object and its backdrop. The soft mask is typically stored independently of the object being composited. In many printing applications, however, the print data stream may comprise of an image and a soft mask of differing dimensions. Accordingly, there is a need for systems and methods to process print data streams where the dimensions of the image and soft mask are different.